The present invention relates to a method of producing active cathode material for lithium secondary battery having the composition, Li.sub.x Ni.sub.y M.sub.1-y O.sub.2.
In recent years, with the progress of the electronic technology, high performance, compact and portable electronic equipment is now available. Secondary batteries used in this modern, compact, portable high performance electronic equipment are required to have high energy density.
Previously, nickel cadmium batteries and lead batteries were employed as the secondary batteries used in these kinds of modern electronic equipment. These batteries have a relatively low discharge potential, however, and therefore are insufficient in providing required high energy density characteristics.
Recently, research and development efforts have lead to the development of lithium secondary batteries in which a material capable of doping and de-doping lithium ion, such as, for example, lithium, lithium alloy or carbon material is used as active anode material. Lithium compound oxides, such as, for example, lithium cobalt compound oxide, lithium nickel compound oxide or lithium nickel cobalt compound oxide, etc. are used as active cathode material. A lithium electrolyte, such as LiClO.sub.4, dissolved in a non-aqueous solvent is used as the electrolytic solution.
This modern type of lithium secondary battery has high battery voltage, high energy density, less self-discharge, and excellent cycling characteristics. It has been confirmed that, among the above-mentioned materials, employment of lithium nickel compound oxide (LiNiO.sub.2) as the cathode provides higher energy as compared to employment of lithium cobalt compound oxide (LiCoO.sub.2) as indicated by U.S. Pat. Nos. 4,302,518, 4,357,215 and 4,980,080. In addition, nickel is more abundant than cobalt as a raw material and is therefore inexpensive. Accordingly, development of a lithium secondary battery using lithium nickel compound oxide or lithium nickel cobalt compound oxide including higher percentages of a nickel component than a cobalt component provides cost-savings advantages.
However, in lithium secondary batteries using lithium nickel compound oxide or lithium nickel cobalt compound oxide including high composition ratio of the nickel component, there is a tendency for battery capacity to exhibit undesirable unevenness, such that these kinds of secondary batteries disadvantageously fail to maintain prescribed levels of quality.
It is believed that the reason why the uneven capacity problem occurs is that in lithium nickel compound oxide or lithium nickel cobalt compound oxide including high composition ratios of a nickel component, the exact composition of the compound oxides varies, dependent upon the synthetic conditions present at the synthetic stage and accordingly, it is difficult to obtain lithium secondary batteries having uniform capacity characteristics. In order to provide lithium secondary batteries having higher energy and wherein unevenness of battery capacity is suppressed, it is indispensable to develop a new and improved method for making lithium nickel compound oxides or lithium nickel cobalt compounds including a high composition ratio of nickel component having a substantially uniform composition.